The present invention relates to a tooth coating composition.
The makeup of teeth is generally conducted by applying a composition containing a dye or pigment to the teeth.
For example, dental adhesives and the like have been known as means for applying such a composition to the teeth. These means are such that a monomer is applied to the teeth and polymerized in a short period of time by irradiation of ultraviolet light or heating for the purpose of enhancing the adhesive strength so as to keep the coating over a long period of time (for example, Japanese Patent Application Laid-Open Nos. 69494/1978 and 113089/1977).
On the other hand, the makeup of teeth requires such moderate adhesive strength that the coating is not easily peeled by eating and drinking, but can be easily removed if necessary. However, the application by the above-described dental adhesive is difficult to control the adhesive strength and the degree of application.
Accordingly, it is an object of the present invention to provide a tooth coating composition having such moderate adhesive strength that the coating is not easily peeled by eating and drinking, but can be easily removed if necessary.
The present inventors have found that a tooth coating composition comprising a film-forming polymer containing at least one carboxyl group or the like and having respective specific solubilities in water and ethanol, and water or/and a lower alcohol has moderate adhesive strength.
According to the present invention, there is thus provided a teeth coating composition comprising (A) a polymer having one or more carboxyl (xe2x80x94COOH) or carbonyloxycarbonyl (xe2x80x94COOCOxe2x80x94) groups in its molecule, a weight average molecular weight of 10,000 to 5,000,000, a solubility of 1 g or higher in 100 g of absolute ethanol at 20xc2x0 C. and a solubility of 10 g or lower in 100 g of water at 20xc2x0 C., and (B) water or an alcohol having 1 to 5 carbon atoms.
According to the present invention, there is also provided a method for coating teeth, which comprises applying the tooth coating composition described above to teeth.
According to the present invention, there is further provided use of the polymer (A) described above for coating teeth.
The polymer (A) useful in the practice of the present invention has one or more carboxyl or carbonyloxycarbonyl groups in its molecule, and is preferably a polymer having, as a main chain, a chain obtained by polymerizing polymerizable vinyl group, and one or more carboxyl or carbonyloxycarbonyl groups at its side chains.
The side chain of the polymer (A) may have any other group than the carboxyl or carbonyloxycarbonyl group, and may have any other group than a phosphoric acid residue, for example, a sulfonic, hydroxyl or amide group.
Examples of the polymer (A) include homopolymers and copolymers having a structural unit represented by the following formula (1): 
wherein R1 and R2 are the same or different from each other and are independently a hydrogen or halogen atom or a hydrocarbon group which may be substituted by a halogen atom, and at least one of R3 and R4 are the same or different from each other and are independently a group substituted by a carboxyl or carbonyloxycarbonyl group through an organic group, and the other group is a hydrogen or halogen atom or a hydrocarbon group which may be substituted by a halogen atom, with the proviso that R3 and R4 may form together a carbonyloxycarbonyl group.
Preferable examples of the polymer (A) include homopolymers and copolymers having a structural unit represented by the following formula (2): 
wherein R5 is a hydrogen atom or a hydrocarbon group which may be substituted by a halogen atom, X is xe2x80x94COOxe2x80x94 or xe2x80x94CON(R6)xe2x80x94, in which R6 is a hydrogen atom or an alkyl group, A1 is a single bond or a hydrocarbon group which may be substituted by a halogen atom, B1 is a single bond, xe2x80x94OCOxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94NHCOxe2x80x94 or xe2x80x94CONHxe2x80x94, or may represent a polyalkyleneoxy or poly(alkyleneoxy)carbonyl group together with A1, and Y is a hydrogen atom, a carboxyl group, an aryl group substituted by 1 to 3 carboxyl groups, an alkyl or alkenyl group substituted by 1 or 2 carboxyl groups, or a carbonyloxycarbonyl-substituted aryl group.
In the formula (2), xe2x80x94COOxe2x80x94 is preferred as X. A single bond or a linear or branched alkylene group having 1 to 20 carbon atoms is preferred as A1, and a single bond or xe2x80x94OCO is preferred as B1. It is also preferred that A1 and B1 represent a poly(alkyleneoxy)carbonyl group together with each other. As Y, is preferred a hydrogen atom, a phenyl or naphthyl group substituted by 1 to 3 carboxyl groups, a C1-4 alkyl or alkenyl group substituted by 1 or 2 carboxyl groups, a naphthalenedicarboxylic acid anhydride residue or a phthalic acid anhydride residue.
Preferable other examples of the polymer (A) include homopolymers and copolymers having a structural unit represented by the following formula (3): 
wherein R7 and R8 are the same or different from each other and are independently a single bond or an organic group which may be substituted.
In the formula (3), it is particularly preferred that R7 and R8 are the same or different from each other and are independently a single bond or a C1-20 alkylene group.
Examples of another monomer in the case where the polymer (A) is a copolymer having the structural unit of the formula described above include other monomers than the carboxyl and carbonyloxycarbonyl groups, which may have a functional group. For example, one or more of (meth)acrylates (C1 to C18 alkyl esters, C2 to C18 alkenyl esters, cycloalkyl esters, alkoxyalkyl esters, cyclic ether esters, phenoxyalkyl esters, dialkylaminoalkyl esters, polyoxyalkylene esters, etc.), (meth)acrylamides (amides, alkylamides, dialkylamides, etc.), aliphatic vinyls (C1 to C24 aliphatic vinyls, etc.), styrene monomers (styrene, alkylstyrene monomers, etc.), vinylpyridine monomers, vinylpyrrolidone monomers and maleimides (N-phenyl- maleimide, etc.) may also be used. Examples of monomers having a sulfonic acid residue include 2-acrylamide-2-methylpropanesulfonic acid and sodium styrenesulfonate. These other monomers are preferably used in a proportion of about 2 to 10% of the whole monomer.
The weight average molecular weight of the polymer (A) is 10,000 to 5,000,000, preferably 10,000 to 1,000,000, more preferably 15,000 to 500,000, most preferably 20,000 to 200,000. If the weight average molecular weight is lower than 10,000, the strength of a coating formed on teeth becomes low, and so its durability is insufficient. If the weight average molecular weight is higher than 5,000,000, such a polymer is hard to be dissolved in a solvent, and so any tooth coating composition is hard to be prepared.
The polymer (A) must have such characteristics that the solubility in 100 g of absolute ethanol is 1 g or higher at 20xc2x0 C. and the solubility in 100 g of water is 10 g or lower at 20xc2x0 C. If the solubility in ethanol is lower than 1 g, any tooth coating composition is hard to be prepared. If the solubility in water exceeds 10 g, the water resistance of such a polymer is low, and so the durability of the resulting coating becomes insufficient. No upper limit is imposed on the solubility in absolute ethanol so far as it is 1 g or higher. On the other hand, the polymer (A) may be insoluble in water so far as the solubility in water is 10 g or lower. Incidentally, the solubility of a polymer in absolute ethanol is determined in the following manner. The polymer (10 g) is added to absolute ethanol (100 g), and the mixture is stirred at 20xc2x0 C. for 1 hour. The remaining polymer is then separated by filtration to measure its weight, thereby finding an amount of the polymer dissolved from a difference between the weight of the polymer before the dissolution and the weight of the remaining polymer. The solubility of the calcium salt of the polymer is determined in the following manner. Calcium chloride in an equimolar amount to a carboxyl and/or phosphoric group in the polymer is added to a polymer solution prepared in the above-described manner. The mixture is then stirred at 20xc2x0 C. for 1 hour. Thereafter, a polymer precipitated is separated by filtration to measure its weight, thereby finding an amount of the polymer dissolved from a difference between the weight of the polymer before the dissolution and the weight of the polymer precipitated.
The polymer (A) is preferably such that its calcium salt has a solubility of 2 g or lower in 100 g of water at 20xc2x0 C. and a solubility of 1 g or higher in 100 g of absolute ethanol at 20xc2x0 C. When the tooth coating composition according to the present invention is applied to teeth, the polymer (A) reacts with calcium on the surfaces of the teeth or in saliva in the mouth to form a salt. Accordingly, the polymer may preferably be a water-soluble polymer having a solubility of 10 g or lower so far as it forms a salt with calcium to lower its water-solubility, thereby improving its water resistance, because its durability in the mouth is enhanced. A more preferable solubility of the calcium salt in 100 g of water at 20xc2x0 C. is 0.5 g or lower, while a more preferable solubility in absolute ethanol 100 g at 20xc2x0 C. is 2 g or higher. Moderate durability and removability when intended to be removed can be imparted to the coating agent according to the present invention as far as the polymer (A) has such solubility characteristics.
The acid value of the polymer (A) is preferably at least 0.1, particularly 0.1 to 700 from the viewpoints of adhesive property to teeth and durability of a coating.
The polymer (A) is preferably incorporated in a proportion of 1 to 70% by weight (hereinafter indicated merely by xe2x80x9c%xe2x80x9d), particularly 5 to 40% in the composition according to the present invention.
The composition according to the present invention is provided in the form of a dispersion by incorporating (B) water or an alcohol having 1 to 5 carbon atoms into the polymer (A). The alcohol having 1 to 5 carbon atoms is a linear or branched, saturated alcohol. Among others, ethanol and isopropyl alcohol are preferred, with ethanol being particularly preferred. Two or more components selected from water and these alcohols may also be used in combination. Water or these alcohols are preferably incorporated in a proportion of 30 to 98%, particularly 50 to 95% based of the total weight of the composition.
Into the composition according to the present invention, is preferably incorporated an inorganic pigment such as mica titanium, titanium oxide or powder of shell, or an organic pigment such as fish scale guanine for the purpose of imparting aesthetic property and gloss (luster) to teeth.
With respect to mica titanium used in the present invention, that having an average particle diameter of 1 to 200 xcexcm is preferably used from the viewpoint of aesthetic property and gloss (luster). That having an average particle diameter of 10 to 100 xcexcm is particularly preferred. With respect to titanium oxide, that having an average particle diameter of 5 nm to 5 xcexcm is preferably used by the same reason as described above. That having an average particle diameter of 10 nm to 0.5 xcexcm is particularly preferred. Mica titanium and titanium oxide may be used either singly or in combination.
The amount of these powders added to the composition according to the present invention is preferably 0.1 to 10%, more preferably 0.2 to 5% from the viewpoints of gloss-imparting property and even coating property.
A blending ratio of the polymer (A) to mica titanium and/or titanium oxide is preferably 1:0.01 to 1:1 in terms of weight ratio from the viewpoints of gloss-imparting property and even coating property.
Into the composition according to the present invention, may be further added various kinds of powder. For example, a-quartz, silica, alumina, hydroxyapatite, calcium carbonate, fluoroaluminosilicate glass, barium sulfate, zirconia, glass, ultrafine silica, and organic composite powder containing an organic component and an inorganic component may be used. Powder of polymers such as polymethyl methacrylate, copolymers of methyl methacrylate and a crosslinkable monomer, polystyrene and polyvinyl chloride may also be added as needed.
Into the composition according to the present invention, may be further incorporated various kinds of publicly known ingredients, for example, dentine reinforcing agents such as sodium monofluorophosphate, tin fluoride and sodium fluoride; germicides; pH adjusters, enzymes; anti-inflammatory agents and blood circulation-facilitating agents; sweeteners; colorants and coloring matter; and perfume bases.
The composition according to the present invention can be provided in accordance with a method known per se in the art, for example, by mixing the polymer (A) and the component (B), and optionally the above-described pigment, a thickener such as ethyl cellulose, hydroxypropyl cellulose or carboxyvinyl polymer, and the like.
The composition according to the present invention can be caused to adhere to teeth by applying it to the teeth in accordance with a method known per se in the art and evaporating a solvent component. The tooth coating agent adhered to the teeth can be easily removed by means of ethanol or the like.
The viscosity of the composition according to the present invention upon its application to teeth is preferably 2 to 500 mPa.s, particularly 5 to 200 mPa.s. If the viscosity is lower than 2 mPa.s, there is a possibility that the composition may drip in or out the mouth. If the viscosity is higher than 500 mPa.s on the other hand, the spreading of the composition becomes poor, and so it is difficult to evenly apply the composition to the surfaces of teeth. The viscosity of the composition as used herein means a value measured by a Brookfield type viscometer.